Mapping Atomic Motions with Electrons: Toward the Quantum Limit to Imaging Chemistry

Recent advances in ultrafast electron and X-ray diffraction have pushed imaging of structural dynamics into the femtosecond time domain, that is, the fundamental time scale of atomic motion. New physics can be reached beyond the scope of traditional diffraction or reciprocal space imaging. By exploiting the high time resolution, it has been possible to directly observe the collapse of nearly innumerable possible nuclear motions to a few key reaction modes that direct chemistry. It is this reduction in dimensionality in the transition state region that makes chemistry a transferable concept, with the same class of reactions being applicable to synthetic strategies to nearly arbitrary levels of complexity. The ability to image the underlying key reaction modes has been achieved with resolution to relative changes in atomic positions to better than 0.01 Å, that is, comparable to thermal motions. We have effectively reached the fundamental space-time limit with respect to the reaction energetics and imaging the acting forces. In the process of ensemble measured structural changes, we have missed the quantum aspects of chemistry. This perspective reviews the current state of the art in imaging chemistry in action and poses the challenge to access quantum information on the dynamics. There is the possibility with the present ultrabright electron and X-ray sources, at least in principle, to do tomographic reconstruction of quantum states in the form of a Wigner function and density matrix for the vibrational, rotational, and electronic degrees of freedom. Accessing this quantum information constitutes the ultimate demand on the spatial and temporal resolution of reciprocal space imaging of chemistry. Given the much shorter wavelength and corresponding intrinsically higher spatial resolution of current electron sources over X-rays, this Perspective will focus on electrons to provide an overview of the challenge on both the theory and the experimental fronts to extract the quantum aspects of molecular dynamics

ASSESSING THE IMPACTS OF CLIMATE CHANGE ON THE HYDROLOGY OF THE INDRAWATI RIVER BASIN, NEPAL

Abstract. This study details climate change assessment of the hydrological regime of Indrawati basin of Nepal. The study uses Soil and Water Assessment Tool (SWAT) model to delineate, discretize and parameterize the Indrawati basin to compute model's input parameters. The model was then run for 1990–2014 to simulate the discharge at the outlet (Dholalghat). The coefficient of determination R2 and Nash-Sutcliffe (ENS) were used to evaluate model calibration and validation. The results found were satisfactory for the gauging station R2 = 0.951 and ENS = 0.901 for calibration and R2 = 0.937 and. ENS = 0.906 for validation. The calibrated hydrological model was run for the future climate change scenario using the RegCM4-LMDZ4 data and the relative changes with the baseline scenarios were analyzed. The comparison suggests that the historical trend of flow is decreasing at the rate of 0.55 m3/s per year. According to RegCM4-LMDZ4 simulations, the trend is going to continue but at a flatter rate. The decreasing trend is observed to be very less. The characteristic peak flow month in the historical scenario is August but the RegCM4-LMDZ4 led simulated flows suggest a shift in monthly peak to October suggesting decrease in monsoon flows and a subsequent significant increase in flows from October to January

Hyperheavy nuclei: existence and stability

What are the limits of the existence of nuclei? What are the highest proton numbers $Z$ at which the nuclear landscape and periodic table of chemical elements cease to exist? These deceivably simple questions are difficult to answer especially in the region of hyperheavy ($Z\geq 126$) nuclei. We present the covariant density functional study of different aspects of the existence and stability of hyperheavy nuclei. For the first time, we demonstrate the existence of three regions of spherical hyperheavy nuclei centered around ($Z\sim 138, N\sim 230$), ($Z\sim 156, N\sim 310$) and ($Z\sim 174, N\sim 410$) which are expected to be reasonably stable against spontaneous fission. The triaxiality of the nuclei plays an extremely important role in the reduction of the stability of hyperheavy nuclei against fission. As a result, the boundaries of nuclear landscape in hyperheavy nuclei are defined by spontaneous fission and not by the particle emission as in lower $Z$ nuclei. Moreover, the current study suggests that only localized islands of stability can exist in hyperheavy nuclei.Comment: 13 pages (including supplementary information), submitted to Physics Letters B, revised version of the manuscript with some additional information include

Comparison of concentration methods for quantitative detection of sewage-associated viral markers in environmental waters

Pathogenic human viruses cause over half of gastroenteritis cases associated with recreational water use worldwide. They are relatively difficult to concentrate from environmental waters due to typically low concentrations and their small size. Although rapid enumeration of viruses by quantitative PCR (qPCR) has the potential to greatly improve water quality analysis and risk assessment, the upstream steps of capturing and recovering viruses from environmental water sources along with removing PCR inhibitors from extracted nucleic acids remain formidable barriers to routine use. Here, we compared the efficiency of virus recovery for three rapid methods of concentrating two microbial source tracking (MST) viral markers human adenoviruses (HAdVs) and polyomaviruses (HPyVs) from one liter tap water and river water samples on HA membranes (90 mm in diameter). Samples were spiked with raw sewage, and viral adsorption to membranes was promoted by acidification (method A) or addition of MgCl2 (methods B and C). Viral nucleic acid was extracted directly from membranes (method A), or viruses were eluted with NaOH and concentrated by centrifugal ultrafiltration (methods B and C). No inhibition of qPCR was observed for samples processed by method A, but inhibition occurred in river samples processed by B and C. Recovery efficiencies of HAdVs and HPyVs were ∼10-fold greater for method A (31 to 78%) than for methods B and C (2.4 to 12%). Further analysis of membranes from method B revealed that the majority of viruses were not eluted from the membrane, resulting in poor recovery. The modification of the originally published method A to include a larger diameter membrane and a nucleic acid extraction kit that could accommodate the membrane resulted in a rapid virus concentration method with good recovery and lack of inhibitory compounds. The frequently used strategy of viral absorption with added cations (Mg(2+)) and elution with acid were inefficient and more prone to inhibition, and will result in underestimation of the prevalence and concentrations of HAdVs and HPyVs markers in environmental waters

Viewpoint – Pouring money down the drain: Can we break the habit by reconceiving wastes as resources?

As water-sector professionals re-discover the value in the 'waste' conveyed in 'waste'water, this Viewpoint argues that the theory of plural rationality (also known as Cultural Theory) may accelerate the switch from waste management to resource recovery. Accordingly, it extends the framing of plural rationality, from its traditional applications in matters of governance and social and economic analysis, to the beginnings of a set of plural schools of engineering thought. This sounds controversial. Indeed, we hope it is. For all too often ways to resolve water issues end up in the impasse of two deeply entrenched positions: the 'technocratic reductionism' of the 'quick engineering fix' to problem solving; and the 'participatory holism' of the 'local, socially sensitive, integrationist' approach. Plural rationality sees this is an impoverished duopoly. Our very strong preference is to find ways of promoting the creative interplay among plural (more than two), mutually opposed, contending ways of framing a problem and resolving it. This, we argue, should not only expand the portfolio of possible alternatives for technology-policy interventions, but also lead to the chosen alternative being preferable — in social, economic, and environmental terms — to what might otherwise have happened. Such solutions are called 'clumsy' in plural rationality theory. We use a synopsis of a case history of restoring water quality in the River Rhine in Europe, within a wider account of the sweep of resource recovery spanning two centuries (late 18th Century through early 21st Century), to illustrate how clumsiness works. This, however, does not extend to our elaborating our proposed set of plural schools of engineering thought beyond just its very beginnings. Our Viewpoint allows us merely to start framing the challenge of developing, and eventually applying, such a notion

Plant breeding can be made more efficient by having fewer, better crosses

BACKGROUND: Crop yields have to increase to provide food security for the world’s growing population. To achieve these yield increases there will have to be a significant contribution from genetic gains made by conventional plant breeding. However, the breeding process is not efficient because crosses made between parental combinations that fail to produce useful varieties consume over 99% of the resources. RESULTS: We tested in a rice-breeding programme if its efficiency could be improved by using many fewer, but more judiciously chosen crosses than usual. In a 15-year programme in Nepal, with varietal testing also in India and Bangladesh, we made only six crosses that were stringently chosen on complementary parental performance. We evaluated their success by the adoption and official release of the varieties they produced. We then modelled optimum cross number using assumptions based on our experimental results. Four of the six crosses succeeded. This was a fifty-fold improvement over breeding programmes that employ many crosses where only about one, or fewer, crosses in 200 succeed. Based on these results, we modelled the optimum number of crosses by assuming there would be a decline in the reliability of the breeder’s prediction of the value of each cross as more crosses were made (because there is progressively less information on the traits of the parents). Fewer-cross programmes were more likely to succeed and did so using fewer resources. Making more crosses reduced the overall probability of success of the breeding programme. CONCLUSIONS: The efficiency of national and international breeding programmes would be increased by making fewer crosses among more carefully chosen parents. This would increase the number of higher yielding varieties that are delivered to farmers and hence help to improve food security